Computing trends since the dawn of the personal computer have gone in one direction: smaller and more portable. Laptops have become the majority of sales for Mac and Windows computing devices, but their total sales figures are dwarfed by two new entries in the realm of personal computing: the tablet and the smartphone.
Laptops and Desktops
Laptop computers, in their modern clamshell configuration, have always made a trade-off between power (and heat), battery life, and size. For more than a decade, if you wanted real computing power, you went with a desktop, which had a more powerful processor, a larger hard drive and more RAM. As of mid-2014, this trade-off has become much less stark; desktops still hold an edge in the maximum amount of RAM allowed, and a slight edge in CPU performance. Current generation laptops are powerful enough to run any business software, Web browsers and email clients, with batteries that will last most of a day of general usage. Only specialized programs, like 3D rendering systems, or high end video editing suites, require enough computing cycles to require a desktop computer.
The Rise of Tablets
Tablet computers, starting with the iPad and its Android analogues, are a direct outgrowth of advances in lower power processors and capacitive touch screen technology. While Microsoft had been trying (unsuccessfully) to make the tablet computer work since 2000, it was Apple's iPad that was the first such successful product. Now, tablet computers are, to a limited extent, doing what laptops did to the desktop computer: making them a specialized tool that's only used when its capabilities are needed. The trade-off between tablets and laptops is two-fold -- tablets are lighter, and (with few exceptions) have less capable hardware than a laptop. In return, they are less useful for content creation – they don't come with a dedicated keyboard, which makes writing reports, articles or school papers more difficult, and many major creation programs like Adobe Illustrator don't have a tablet-friendly version.
Smaller Yet -- The Smartphone
Nearly every argument for a tablet over a laptop can be made for a smartphone over a tablet – the smartphone is smaller, and the computer you have on you is the one you'll use. One drawback is that smartphones run into screen size and battery life issues compared to tablets. Still, most of the apps you can run on a tablet also have smartphone versions, and if your primary computing use is surfing the Web or checking Facebook, a smartphone may be all that you need in a computing device. Most Web sites and content are easier to read and use on a tablet or a laptop, and laptops are vastly superior for entering text, doing photo manipulation and doing productive work.
There are a handful of devices, most prominently the Microsoft Surface series, that try to hybridize the laptop and tablet. These are meant to be lighter than a laptop, and use a touch-screen interface for most uses and an attachable keyboard when serious typing is needed. The Microsoft Surface line of hybrids had two versions – the Surface RT, using an ARM-based processor (like the iPad) and the Surface Pro, using an Intel-based processor (like most laptops). While both used a version of Windows 8, applications written for the Surface Pro do not run on the Surface RT and vice versa. As of mid-2014, Microsoft is putting most of its marketing efforts behind the Surface Pro line, which has the largest reservoir of compatible software. While its current incarnation isn't the runaway success the iPad was, the Surface Pro is a likely evolution of the laptop going forward.